Electrostatic printing system



'March 19, 1963 c, o. CHILDRESS ETAL 3,081,693

. ELECTROSTATIC PRINTING SYSTEM Filed March 4, 1960 2 Sheets-Sheet 2 vol. Z065 sup/=4 1 $00065 uvwszvroas United States Patent 3,081,698 ELECTROSTATIC PRINTING SYSTEM Clyde 0. Childress and Louis J. Kabell, Palo Alto, Calif.,

assignors, by mesne assignments, to Electrostatic Printing Corporation of America, San Francisco, Calif.,

a corporation of California Filed Mar. 4, 1960, Ser. No. 12,714 14 Claims. (Cl. 101-129) This invention relates to electrostatic printing, and, more particularly, to an improved method and means thereof, which requires neither pressure nor contact between the printing element and the subject material being printed.

Presently employed printing techniques involve the transfer of liquid inks to paper by a plate or a cylinder, utilizing either raised areas or chemically active areas to carry the ink. These methods have in common the handling and feeding of viscous pigments smoothly to the printed surface. Considerable pressure is required to transfer the ink to the paper, and printing surfaces must be maintained level to very close tolerances, on the order of .001 inch, to maintain even ink transfer. The wet ink must be dried quickly. As a result, and this is true particularly in high-speed printing, it is required that a printing press must be massive, complex, and able to operate with extreme precision.

An object of this invention is to provide a novel printing method that eliminates the requirements of pressure and uniformity of contact or any contact at a printing surface.

Another object of this invention is to provide a unique printing method and means wherein the apparatus has a considerably lessened size and weight from that of conventional presses.

Still another object of the present invention is the provision of a unique electrostatic printing method and means which enables a simultaneous printing of both sides of a sheet of paper or other object being printed.

These and other objects of the invention are achieved in an arrangement wherein there is provided an electrically charged conductive stencil wherein the printing areas comprise a fine-mesh open screen and the nonprinting areas are suitably masked. The paper being printed may be backed by a conductive plate with an opposite charge relative to the charge of the printing stencil. A finely divided printing powder having a particle size capable of passing through the open areas of the stencil, is applied to the face of the stencil opposite to the conductive backing plate, where it takes on the charge of the stencil and by means of the relatively low voltage electrostatic forces established, passes through the openings therein, across an air gap and toward the oppositely charged plate. However, the paper placed in the air gap of the electrostatic field intercepts the printing powder, and the printing powder forms the image thereon of the open areas of the printing stencil. The image can then be fixed in any suitable manner such as by heat, solvent, vapor, or by any other suitable means.

If printing on both sides of the paper is required, then there are provided two closely spaced conductive stencils which are oppositely charged, and the paper, is positioned between these conductive stencils but appropriately spaced from each other. The finely divided printing powder is applied to the outer faces of both stencils or screens. When the electrostatic field is set up the powder from one stencil will be attracted toward the other, through the open areas of each, resulting in the interception by the paper which is thereby printed on both sides.

If a printing powder made of nonconductive particles is employed, then it is possible to print directly onto the backing conductive plate, whatever material it may hap- 3,081,698 Patented Mar. 19, 1963 pen to be, so long as it is conductive or rendered conductive. Thus, this system also provides an arrangement for printing on metal, as well as on paper or other materials.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawings, in which:

FlGUREl illustrates an embodiment of the invention;

FIGURE 2 illustrates an embodiment of the invention for printing rapidly on both sides of the paper;

FIGURE 3 illustrates an embodiment of the invention utilizing a cylindrical stencil;

FIGURE 4 illustrates an embodiment of the invention using two'cylindrical stencils for printing on both sidesof the paper; and

FIGURE 5 illustrates still another arrangement employing the embodiment of the invention for printing both sides of the paper.

Reference is now made to FIGURE 1, wherein there may be seen the simple arrangement of an embodiment of the invention. .It includes a printing element or stencil 10 which may comprise a fine-mesh open screen of conductive material or material which is rendered conductive, wherein the nonprinting areas are suitably masked. Spaced therefrom leaving an air gap therebetween, is a sheet of paper 12 on which the printing is to occur. This is backed by a conductive plate 14. A source of directcurrent potential 16 has one end thereof connected to the printing element 10 and the other end connected ,to the backing plate 14. Since the plate and stencil are oppositely charged by the voltagesupply source an electric field is established in the air gap between the two within which the paper 12 has been placed.

A pigment (not shown) in the form of a fine powder having a particle size small enough to pass through the interstices of the open areas of the stencil *10 may be brought into physical contact with the back of the stencil .10, by means of a roller 18 or other suitable applicator. The roller, a felt-like type of covering 19, which can be dipped into a suitable container of the fine powder so that the powder will loosely adhere to the surface thereof. The roller is then rolled over the outer surface of the stencil. When the voltage is applied as the pigment particles contact the conductive stencil, they acquire a charge, which is that of the stencil. The charge being opposite to the backing plate, they then are accelerated through the openings or interstices of the open areas in the stencil toward the other plate 14, which has an opposite charge. However, thepigment will collide with the interposed paper and will collect and adhere there in the form of a visible image or configuration of the open areas of the said stencil. As pointed out, the image may be subsequently fixed by heat, a solvent, or a vapor, or by any other suitable means, depending upon the type of pigment powder which has been employed, and the nature of the material being printed.

A suitable method for making the conductive printing stencil may be as follows: An electro-formed nickel screen with 250 wires to the inch is coated with a photosensitive resist. 'Ihis coating is applied so that it spans all the interstices in the screen. The sensitized screen is then exposed to an are (one rich in ultraviolet light) through an interposed positive image of the desired copy for the proper length of time to harden the areas where the interposed image transmits light. The coated screen is then developed, which development will dissolve away the areas of resist which were protected from the light by the opaque areas of the film image, leaving a solid mask in the areas affected by the light. The printing element so formed is mounted in a suitable holder and connected with either the positive or negative pole of a direct-current source of voltage.

The oppositely charged conductive backing plate 14, with the paper 12 to be printed upon adjacent to it, is positioned so that the surface of the printing stencil is parallel to and spaced approximately one-sixteenth of an inch from the surface of the paper leaving an air gap therebetween. A voltage from the source 16 is applied between the screen and the plate sufficient to provide a satisfactory transfer of the pigment, but below the arcing potential between the charged elements. The optimum voltage is determined by the width of the air gap and the characteristics of the paper and pigment used. The use ful voltage range may lie between 300 volts and 2000 volts but relatively low voltages are entirely satisfactory for most uses.

As stated previously, the pigment powder is brought into contact with the stencil by a soft roller, brush or other suitable means. The pigment powder particles which contact the screen take on the charge of the screen and are attracted toward the opposite charge of the backing plate, and, as a result, are intercepted by the paper. These particles tend to follow the parallel field lines and thus travel across the air gap from screen to paper with very little dispersion. The paper upon which the image is to be printed does not have to contact the charged backing plate. The invention operates equal-1y, regardless of which voltage polarity is applied to the stencil and backing plate, so long as they are opposite. Consequently, it is possible to substitute a stencil printing element for the backing plate and print simultaneously on both sides of the paper, which is placed substantially equally distant from the screens.

Various methods of preparing the stencil can be used. 'It is merely necessary that the nonprinting areas be eifectively masked to prevent the movement of the pigment therethrough. This can be accomplished by various wellknown hand methods, as well as by the use of photosensitive coatings on the open mesh. Techniques familiar in the silk-screen process may also be used. It is not necessary to have the regularity of openings. of a fine mesh screen or sensitized net. The irregular openings in fibrous materials and the like are satisfactory so. long as the openings and the particle size of the pigment are compatible for movement therethrough.

Other materials may be printed upon, employing the embodiment of the invention shown, than paper. Rubber, fabric, ceramics, and plastics are illustrations of such other material. Even metal may be printed upon. This is done by omitting the paper or other material and using a pigment having nonconductive particles. The conductive material is substituted for .the backing plate 14 and provides the surface upon which printing occurs. Thus, after such printing, the image on the substituted material may then be fixed in a similar manner as was described for fixing the image on paper. The explanation of what occurs when printing on metal is. done, as best understood, seems to be that each of the nonconductive pigment particles receive a plurality of isolated charges over their surfaces from the charged stencil. These particles are then drawn through the stencil to the metal plate 14. There the portion of these particles which strike the metal. plate give up their charges, but the remaining charges on. the surfaces of the particles not in contact with the metal plate are sufiicient to cause the particles to adhere to the metal plate until permanently affixed thereto.

An arrangement for the invention, whereby continuous printing on both sides of the, paper may be effectuated, is shown in FIGURE 2.- The paper 20. is fed continuously from: a roll 22 between both printing members 24, 26.

The printing stencil members are in the form of loops.

and are made of a suitable flexible conductive material, such as the electro-formed nickel screen. The loops are rotated to move synchronously with the paper passing 4.- therebetween. The printing stencil member 24 is mounted on the rollers 28, 32, and the stencil printing member 26 is mounted on the rollers 30, 34. These various rollers are driven by any well-known means (not shown) to effectuate the required synchronous motion. A voltage supply source 36 makes contact with the stencil printing members to give them opposite polarities by means of leads connected to the respective brushes 38, 40.

Inside each of the loops formed by the stencil printing members are the respective brush rollers 42, 44. These rotate in contact with the inner face of the stencil printing members, applying the printing powder thereto, which is picked up from containers or troughs 46, 48 supported adjacent the roller brushes and in which they are in substantially continuous contact.

The paper is passed between the two stencil printing members 24, 26, but not in contact with either of them. The powder delivered by the respective brushes 42, 44 will be drawn through the open areas in the stencil printing members toward the paper 29 as the paper passes through the printing zone defined by the opposed and oppositely charged stencil printing members. The printing members 'are also moved in order to bring their different areas into contact with the roller brushes 42, 44 to effectuate printing. After the paper passes through the printing zone, it passes through a print-"fixing station, accomplished in any suitable manner but which is here exemplified by a plurality of heating wires or elements 50, which are positioned on opposite sides of the paper for fixing the particles which have been directed thereon. The-heating wires have power applied from a source 51.

FIGURE 3 shows another possible arrangement for the embodiment of the invention. For some applications a rotary cylinder press is preferable. In this event, the stencil printing member is in the form of a cylinder or arranged upon a cylinder 52, and the powder applicators 54, 56, 58 are mounted by a support member 60 inside the cylinder to be rotatable and in contact with the inner surface of the stencil printing member. Powder may be blown into the brushes '54, 56, 58 in an arrangement in which the brushes are mounted on hollow axles having openings through which the powder may be blown into the material of the brush. Such expedients are well known in the field of Xerography.

The paper 60 passes underneath the printing zone, which is established between the cylinder with the stencil printing member and the backing plate 62 in the form of a portion of an arc. The paper 60 may be drawn down into a suitable printing configuration, by means of having a plurality of openings in the backing plate and applying a vacuum thereto, using a pipe 61, so that the suction will pull down the paper and maintain it properly spaced from the printing member to maintain the air gap and prevent possible arcing. Alternatively, rims may be placed on the outside edges of the printing-member cylinder which are made of insulating material and space the paper the proper distance away from the cylinder. Rollers 64, 66 serve to support and guide the paper in the printing zone. A voltage supply 68 is connected to the respective printing member and backing member by suitable contacts 67, 69.

FIGURE 4 shows an arrangement for using the cylindrical type of stencil printing member or mounting therefor, and printing continuously on both sides of the paper. The upper-lower cylindrical stencil printing members, respectively 70, 72, are rotatably supported by any suitable means (not shown). Inside'of each cylindrical member 70, 72 is an applicator, respectively 74, 76, which supplies the inner surface of the stencil member with powder. A potential is applied from a source 78 through brushes 77, 79. As the paper moves, the cylindrical-printing members are rotated, and the pigment powder is drawn through the interstices therein toward each other, but intercepted by the paper between them. Here again the paper passes through the air gap between the stencil printing members and without any contact with them.

Although the description of the utility of the embodiment of the invention has thus far shown the stencil printing member comprising a foraminous screen, in flat, cylindrical or loop form, this is merely a way of exemplification, and not to be construed as a limitation upon the invention.

In FIGURE 5 the stencil printing members 80, 82 are shown as being flat and the paper 84 travels in the air gap between them. The paper may be maintained properly spaced from both of the printing members by means of two opposed pairs of rollers 86 A, 863 and 88A, 88B. Voltage is applied to the printing members 80, 82 from a source 90. The pigment applicators this time comprise two cloud chambers 92, 94 which are positioned over the respective areas of the printing members 80, 82 having the perforations defining the printed material desired. The chambers 92, 94 are cloud chambers, into which there is blown a mixture of air and the pigment powder from a pigment supply 96.

The paper 84 is run to and held at the printing station at a suitable rate to allow a printing operation to take place between the stencil printing members 80, 8-2. The voltage is applied only for the fraction of a second required for the printing. A voltage and pigment control 98, which may merely be a clock synchronized with the paper motion, operates suitable relays, not shown, to remove or reduce the voltage applied from the voltage source below powder-transferring values and to remove the pressure under which the pigment supply 96 blows the pigment powder into the chambers 92, 94. The paper, meanwhile, continues moving until a fresh surface for printing is positioned between the printing screens. At this time the voltage and pigment control 98 turns on the voltage and the air pressure to the respective stencils and pigment supply source. The paper on which pigment has been deposited meanwhile advances to a fixing station.

It will be appreciated that the printing means made available by this invention is not limited to letters or symbols, but pictures or any other representations printed today, and even entire areas, may be duplicated using this system. Furthermore, this invention is not to be limited to a single color-printing process. As many different pigment colors as are desired may be laid down, either by employing in sequence a plurality of ditferent screens, each following the other and applying a different color pigment to a different area of the paper previously printed under a preceding screen, or, where a multiple layer of colors is desired, different pigments may be applied in succession to the same screen while the paper remains stationary.

As previously indicated, the voltage range which has been found to work most effectively is from 300 to 2000 volts, depending upon the distance from the screen to the paper, the powder being used, the type of paper, and the humidity. On a typical office-stock bond spaced .02, inch from the screen, 300 volts will transfer the powder; with the spacing increased to .12 inch, 2000 volts will transfer the powder.

It is not necessary that the paper be equally spaced away from the printing element, as long as the voltage is sufficient to print the most distantly spaced parts and not arced to the closer one. Consequently, paper with very rough surfaces or deeply embossed patterns and even corrugated paper, may be printed with sharp detailed images without disturbing the paper texture. A line .005 inch wide has been printed with this invention on grooved paper having valleys .05 inch deep, without impairing the definition of the image at either space extreme.

It has been found that some powder materials are polarity sensitive and will therefore produce better printing for one polarity of voltage on the printing screen. It is believed that the trib'oelectric charging of the particles is responsible for this effect. The effect seems more pronounced for larger particle sizes of highly insulating particles. However, any suitable pigment powder may be employed, such as, for example, carbon black, dry dye powders, and plastic toner. Particle size and degree of powder dispersion are factors in the charging and migration process. At the present time fine powders 'l-l0 micron diameter, solid particles are satisfactory with 500, mesh screen stencils.

. Any suitable arrangement for blocking off the areas of a stencil through which it is not desired the pigment powder to pass, besides the ones mentioned, may be employed. These include masks or stencils made of an insulator such as paper, which is positioned adjacent the screen, preferably on the side against which the powder particles are applied. This makes for rapid interchangeability of the information being printed from a printing member, by the simple expedient of changing the paper stencils which are used with the conductive screen.

Although the arrangement for printing on metal is exemplified in FIGURE 1, which apparently shows a fixed conductive backing plate, it is well within the ability of those skilled in the art to use metal foil, such as silver or aluminum foil, in a roll. This roll then has a potential applied thereto in the manner shown in the plate in FIG- URE l. The foil is then moved past the printing stencil, either continuously or intermittently, much in the manner described for moving the paper rolls herein to afford continuous printing. Of course, the fixing operation followsthe printing operation in the manner previously described.

There has accordingly been described and shown herein a novel printing method and means which does not require pressure to be applied to the surface on which printing is to occur and which is simple, inexpensive, and light in weight. This invention affords a mechanism for printing on the surfaces of conductive materials, such as metal, and nonconductive materials, such as paper, cloth, rubber, plastics, and the like, and on nonconductive materials which through treatment are rendered conductive. These surfaces need not be planar surfaces, since the printing can occur on curved surfaces Within the electric field, or the field itself may be curved by using a curved stencil and/ or backing plate.

The term conductive material as used herein is not to be'understood as limited to materials such as metals, but includes other materials, such as paper, wood, etc., which under certain circumstances of humidity for example, may be considered as conductive. See for ex ample, Patent No. 2,954,291, wherein paper is used as a conductive backing member for a photoconductive insulator coating, or Patent No. 2,847,305 wherein the problems presented by the conductivity of paper in connection with electrostatic deposition are discussed. Accordingly, the term conductive materia as used herein is intended to mean a material that has a sufficient conductivity to cooperate with an opposite electrode when a potential is applied thereto, to establish an electric field which can transfer triboelectric powder in an electrostatic powder transfer system as herein described.

We claim:

1. In an electrostatic printing method having a conductive screen with a plurality of apertures over a portion thereof defining areas desired to be printed, and a conductive member spaced substantially equidistant from said screen and having a surface opposite said screen, said screen and said conductive members being connected in an electric circuit, the steps of applying an electric potential difference to said screen and conductive member to establish and maintain an electrostatic field therebetween, and applying a finely divided pigment powder having a particle size small enough to freely pass through the apertures of said screen to the outer surface of said screen for passage through the apertured portion thereof and into the electrostatic field whereby the pigment powder will move toward and come to rest on said conductive member in a pattern defined by said apertured printing areas of said screen.

2. An electrostatic printing method of claim 1 wherein said conductive member consists of metal foil.

3. In apparatus for electrostatic deposition printing a pair of electrically conductive members connected in an electrical circuit and mounted in spaced substantially parallel relationship with surfaces facing each other leavin an air gap therebetween, at least one of said conductive members being a stencil screen having open areas corresponding to the printing portion and masked areas corresponding to the non-printing portion, a voltage supply source connected in circuit to said conductive members for creating an electric potential difference between said members to establish and maintain an electrostatic field in said air gap, means for disposing a print receiving material in said field spaced from the stencil screen, and means for applying a pigment powder having a particle size to pass freely through the open areas of said stencil screen to the outward surface of the stencil screen for passage through the open areas of said screen into said electrostatic field to be moved under the influence of said field toward the other of said conductive members.

4. In apparatus for electrostatic deposition printing the combination of a pair of electrically conductive members connected in an electrical circuit and in spaced substantially parallel relationship with surfaces facing each other leaving an air gap therebetween, at least one of said conductive members being a stencil screen having open areas corresponding to the printing portion and masked areas corresponding to the non-printing portion, a voltage supply source connected to said conductive members for creating an electric potential difference between said conductive members to establish and maintain a substantially uniform electrostatic field in said air gap, means for applying a powder having a particle size to pass freely through the open areas of the stencil screen to the outward surface of the stencil screen for passage through the open areas of said screen into said electrostatic field to be moved under the influence of said field toward the other of said conductive members, means for interposing a print receiving member in the air gap between the conductive members in spaced relation from said screen to intercept the powder in its passage toward the opposite conductive member, and means for fixing the powder on said print receiving member.

5. In apparatus for electrostatic deposition printing the combination of a pair of electrically conductive members connected in an electrical circuit and mounted in spaced substantially parallel relationship with surfaces facing each other leaving an air gap therebetween, both of said conductive members being stencil screens having open areas corresponding to a desired printing portion and masked areas corresponding to a desired non-printing portion, a voltage supply source connected to said conductive members for creating an electric potential difference between said conductive members to establish and maintain an electrostatic field in said air gap, means for applying powders having a particle size to pass freely through the open areas of the stencil screen to the outward surface of each of said stencil screens for passage through the open areas of each screen into said electrostatic field to be transported under the influence of said field from one toward the other of said stencil screens, and means for interposing a print receiving member in the air gap between the conductive members in spaced relation from said members to intercept the passage of the powders through the open areas of the respective stencils toward each other.

6. In a method for printing electrostatically with a powder upon the surface of material by means of a pair of conductive opposed print forming members spaced from each other and connected in an electrical circuit each having apertured areas defining the printing portions and masked areas defining the non-printing portions, the steps of applying an electric potential difference between said print forming members to establish and maintain an electrostatic field therebetween, applying powders having a particle size to pass freely through the apertures of the print forming members, to the non-opposed surfaces of said print forming members for passage of said powders through said apertured areas of said conductive printing members into said electrostatic field for transport toward the opposite of said opposed conductive members, interp'osing a print receiving material in said field and spaced from each of said print forming members, and fixing the powders intercepted thereby on the surfaces of said material.

7. In an electrostatic printing method recited in claim 6 wherein each conductive print forming member has the shape of a continuous belt, the steps of positioning the print receiving material between and spaced from said opposed print forming members and moving said material between said conductive print forming members in this position, and moving said belts at the speed of motion of the print receiving material and in the direction of its motion.

8. In an electrostatic printing method as recited in claim 6 wherein each conductive print forming member has the shape of a cylinder, the steps of positioning the print receiving material between and spaced from said opposed print forming members and moving said material between said cylinders, and moving said cylinders at the speed of motion of the print receiving material and in the direction of its motion.

9. The method of printing without contact or pressure comprising establishing an electrostatic field between two opposed and uniformly spaced conductive members connected in an electrical circuit, having an area of definite boundaries defined by said members by applying an electric potential between said conductive members, one of said members being a screen stencil with open areas defining the printing portions and masked areas defining the non-printing portions, charging a powder having a particle size to pass freely through the open areas of the screen stencil with the same polarity as the polarity of the potential applied .to said screen, applying said powder to the outer face of said screen, transporting said powder through the open areas of said screen toward the opposite conductive member by means of said electrostatic field, interposing in said electrostatic field without substantially diverting or distorting the same, and spaced from said screen, a print receiving member to intercept the charged powder and obtain the disposition thereof in the areas corresponding to the open areas of said screen, removing the print receiving member from the influence of the electrostatic field with the powder adhering on the surface thereof, and fixing the powder on said surface.

10. In a method of printing without contact or pressure the steps of establishing an electrostatic field between two opposed and uniformly spaced conductive member connected in an electrical circuit, having an area of definite boundaries defined by said members by applying an electric potential difference between said conductive members, one of said members being a screen stencil with open areas defining the printing portions and masked areas defining the non-printing portions, charging a powder having a particle size to pass freely through the open areas of the stencil screen with the same polarity as the polarity of the potential applied to said screen while applying the same to the outward surface of said screen, transporting said powder through the open areas of said stencil toward the opposite conductive member by means of said electrostatic field, and interposing in the said electrostatic field without substantially diverting or distorting the same and spaced from said stencil, a print receiving member to receive the charged powder in accordance with the shape of the open areas of said screen;

ll. Apparatus for electrostatic deposition printing comprising in combination a pair of electrically conductive continuous belt members connected in an electrical circuit and mounted for rotation in opposite directions with a portion of the faces thereof in parallel spaced relation leaving an air gap therebetween, each of said members having a conductive stencil screen with open areas corresponding to the desired printing portions and masked areas corresponding to the desired non-printing portions, means for separately applying a powder having a particle size to pass freely through the open areas of the stencil screens to the interiors of each of the stencils of said belt members and in contact therewith along the zone of parallel movement to pass said powders into said air gap through said open areas, means for moving a print receiving material in the air gap between and spaced from each of said belt members, a source of electrical potential connected to the said belts to establish the belts with opposite polarities and maintain an electrostatic field therebetween, means for synchronizing the movement of said belts with the said means for moving the print receiving material, and means for fixing said powder on said print receiving material positioned beyond the region of rotation of the said belts.

12. in a method of pressureless and contactless printing the steps of preparing a conductive screen stencil having open areas corresponding to the printing areas and masked areas corresponding to the non-printing areas, said screen stencil capable of being placed at a given electrical potential of a given polarity, placing said screen stencil in uniform spaced relation to a conductive member capable of being placed at a given electric potential of opposite polarity to that of said screen stencil, connecting said screen stencil and said member in circuit to a source of electrical potential to establish the opposite polarities and thereby create an electrostatic field therebetween bounded by the dimensions of said screen stencil, interposing a print receiving member in said field between said member and said stencil screen but spaced from said stencil screen, applying a powdered pigment having a particle size to pass freely through the open areas of the stencil screen to the stencil screen on the surface away from the print re ceiving member whereby the powdered pigment of the same polarity as said screen is transported through the open areas of said stencil screen toward the opposite conductive member by means of the electrostatic field, and intercepting the passage of the powdered pigment in said field on said print receiving member.

13. In a method of pressureless and contactless printing the steps of preparing a conductive screen stencil having open areas corresponding to the printing areas and masked areas corresponding to the non-printing areas, said screen stencil capable of being placed at an electrical potential of a given polarity, placing said screen stencil in uniform spaced relation to another conductive member capable of eing placed at a given electric potential of opposite polarity to that of said screen stencil, connecting said screen and said member in circuit to a source of electrical potential to establish the opposite polarities and thereby creating and maintaing an electrostatic field therebetween bounded by the dimensions of said screen stencil, interposing a print receiving member in said field between said screen stencil and said other conductive member but spaced from said screen stencil, applying a powdered pigment having a particle size to pass freely through the openings of said screen stencil to the screen stencil on the surface away from the print receiving member whereby the powdered pigment having the same polarity as said screen stencil is transported through the open areas of said screen stencil toward the opposite conductive memher by means of the electrostatic field, intercepting the passage of the charged powdered pigment in said field on said print receiving member, removing said print receiving member with the intercepted powdered pigment from said electrostatic field, and fixing said powdered pigment on said print receiving member out of the influence of said electrostatic field.

14. In apparatus for electrostatic deposition printing,

an electrically conductive screen having open areas cor-.

responding to the printing portion and masked areas corresponding to the non-printing portion, a voltage supply source, an electrical terminal for connecting a conductive material to be printed upon to said voltage supply source, means spacing said screen from physical and electrical contact with a conductive material to be printed upon to leave an air gap therebetween, means for connecting said voltage supply source in circuit with said screen and said terminal for creating an electric potential difference between the screen and the material to be printed upon to establish and maintain an electrostatic field in the air gap therebetween, and means for applying a pigment powder having a particle size to pass freely through the open areas of said screen to the outward surface of the screen for passage through the open areas of said screen and transport by the electrostatic field across said air gap.

References Cited in the file of this patent UNITED STATES PATENTS 1,784,912 Scott Dec. 16, 1930 1,788,600 Smyser Jan. 13, 1931 2,152,077 Meston et al. Mar. 28, 1939 2,282,203 Norris May 5, 1942 2,551,582 Carlson May 8, 1951 2,590,321 Huebner Mar. 25, 1952 2,784,109 Walkup Mar. 5, 1957 2,792,780 Jacob May 21, 1957 2,901,374 Gundlach Aug. 25, 1959 2,932,690 Adams et a1 Apr. 12, 1960 2,966,429 Darrel et al. Dec. 27, 1960 FOREIGN PATENTS 81,920 Denmark Dec. 27, 1960 692,614 Great Britain June 10, 1953 

1. IN AN ELECTROSTATIC PRINTING METHOD HAVING A CONDUCTIVE SCREEN WITH A PLURALITY OF APERTURES OVER A PORTION THEREOF DEFINING AREA DESIRED TO BE PRINTED, AND A CONDUCTIVE MEMBER SPACED SUBSTANTIALLY EQUIDISTANT FROM SAID SCREEN AND HAVING A SURFACE OPPOSITE SAID SCREEN, SAID SCREEN AND SAID CONDUCTIVE MEMBERS BEING CONNECTED IN AN ELECTRIC CIRCUIT, THE STEP OF APPLYING AN ELECTRIC 